The application of materials to the roots of seedlings prior to transplanting is a known practice. The usual procedure consists simply of dipping the roots of seedlings into a solution of toxicant immediately prior to insertion of the seedling into the proposed growth medium.
This practice is unsatisfactory in many cases, particularly in the case of paddy rice, because the water of the paddy tends to wash off the toxicant before the roots of the seedling can be placed in the soil beneath the water. In many cases, phytotoxicity of the desired compound precludes the intimate contact of the root with the pesticide as would be incurred in the normal manner of dipping roots into solutions of toxicant.
Current pesticide usage by application of the pesticide by spraying from knapsack or boom sprayers, by aerial applications from helicopters, etc., present a number of difficulties. Because the pesticide cannot by these methods of application be placed specifically into the precise areas where protection is essential, the entire field must be treated, and a greater than essential amount of pesticide must be introduced into the environment. This is undesirable both from the standpoint of economics, or purchase of pesticides, and from the standpoint of exposure of the environment to the undue amount of chemical. Because the spraying or dusting is subject to the vagaries of wind, there is also the ever present danger of drift of the applied pesticide into areas where treatment is not needed and may even be quite undisirable. The problems of placement of the pesticide have been particularly important where the site of attack by the undesired organisms is beneath the surface of the soil in the root zone, as, for example, in rice and other transplanted crops.
Attempts to overcome these problems have involved formulating the pesticides into granular particles sufficiently heavy as to be susceptible to wind drift. Seed treatment techniques have been tried with varying sucess. Root-soak and root-coat treatments have been more effective and have led to a variety of attempts to place the pesticides into the root zone using "capsules" made from small sections of paper straw, or "gelatin" capsule, such as are commonly used in pharmaceutical packaging. These provided excellent control but their preparation is extremely tedious and expensive and their individual insertion into the root zone of each individual plant was equally tedious and time-consuming.
A technique for the placing of a pesticide in the root-zone of a pine seedling by previous coating of the root is described by Walstad, Journal of Economic Entomology, Vol. 66, No. 5, pp. 1219-20, October 1973. This technique was experimentally found totally unsatisfactory for use in the case of flexible plants such as rice because the seedling are so flexible that their root systems cannot be dipped into the thick clay slurries. Further, the clay coating rewets so rapidly as to disintegrate before the rice seedling reaches the soil of the paddy in which it is to be planted. And finally, the clay coating in drying desiccates the rice seedling roots to such extent that the seedling cannot survive the treatment.
Pesticides particularly useful for application via root treatment as described herein are those having a good contact insecticidal activity as well as a good systemic insecticidal activity. Outstandingly useful is carbofuran, described in U.S. Pat. No. 3,474,171, issued 1 Oct. 1969 to William G. Scharpf and assigned to FMC Corporation which patent may be considered to be fully incorporated herein.